Thanks, Phil.
I googled it, and all the technique lessons I'm finding involve a pick rather than fingerstyle.

Is he using his thumbpick to rake? If you look later in the video (1:48 mark) he does the same thing and there's a side shot, and it looks like he's using his main fingers, not the thumb. Is it possible to rake using the main fingers rather than the thumb, and is that what he's doing?

He is simply playing quick ascending arpeggios with the fingers as embellishments of the melody notes. The technique is very common in classical quitar playing and possibly originated during the Renaissence, perhaps on the harpsichord.

I disagree with the term "raking", which is generally used to imply dragging a flatpick or a fingernail across multiple strings in quick succession. I agree with those posts which describe this as simply a series of sixteenth notes which are plucked with the fingers on the right hand. Similar, but the technique is different.

I agree with Ric, in that what Chet's doing is in no definition of the term, "raking".....it's a series of individually pic'k notes and yes, more of a banjo roll than anything. When notes are played this quickly they're 'outside' of the melody notes and are used just to augment the melody with a bit of variety. And these added notes do not disrupt the tempo the same way a true banjo roll does. A banjo roll is it's own entity where these extra notes aren't.

A good example of "raking" - a downward sweep of the right hand fingers across the strings - or an upward sweep with either the thumbpick or one finger - usually a part of classical and latin styles played on a nylon string guitar, is Chet's playing of All Thumbs. His version isn't online unfortunately but there's a few passable versions from others you can see.

You guys are absolutely right, as it's not called raking --- the actual term is tirando (free stroke).

I stand corrected!

– Phil T

No...a tirando stroke is something else altogether. In classical guitar there are two basic ways of playing a note. One is called 'apoyando' (also known as a rest stroke, or a supported stroke) in which you play in such a way that the finger comes to rest against the next string down. For example if you hit your top E, and the finger comes to rest against your B.

The other is 'tirando' - which is when the striking finger doesn't come to rest against another string.

The technique in the video is a roll - it is common in classical guitar playing.

If this isn't clear, I'd be happy to do a quick video and put it here for anyone who's interested.

Holy crap, thanks for making that. Would you guys agree this is what he's doing? It does sound and look correct b/c in the video I can see it's something with this three fingers instead of the thumb. How would you count that? Is the thumb 1, and the others e&a for a quick 16th note pattern? Can't quite make out the count. Almost sounds like the final note is early (a tie?) for the next chord. I want to work it out on the metronome so just wondering how to count it.

Edit: this video touches exactly on what I'm talking about:

He mentions either the first note is early or the last late. Can you guys tell which is the case in the Chet piece? Since I can't play the technique correctly yet it's hard to tell.

It's not an exact technique, it's just a feel thing. As with other forms of nuance, it isn't a precise, count it out moment, so just play it by running into it, not just playing the run on its own. Bring it up to speed and you'll have it. The only part of timing that applies here is that this run isn't slowed down and the song's tempo at that point maintained.